The present invention relates to a gateway apparatus, communication system, and delay measurement method and, more particularly, to a gateway apparatus, communication system, and delay measurement method which measure the delay of an IP (Internet Protocol) network.
As a delay measurement method of this type, there has conventionally been proposed measurement by, e.g., a method of generating a special packet for measurement (see, e.g., reference 1 (Japanese Patent Laid-Open No. 2003-244237)), or a method of padding time information in a packet itself (see, e.g., reference 2 (Japanese Patent Laid-Open No. 2001-333092)).
These methods do not use a standard packet defined in the RFC (Request For Comments) of IETF (the Internet Engineering Task Force). In a today's IP network in which network address translation, a packet filter, and priority control are generalized, measurement is not performed under the same conditions as those for an RTP (Real-time Transport Protocol) stream to be measured.
In round-trip measurement using RTCP (RTP Control Protocol) described in RFC3550 (see, e.g., reference 3 (“RTP: A Transport Protocol for Real-Time Applications, 6.4 Sender and Receiver Reports” (RFC3550, July 2003, Pages 35-45)), (1) RTCP must be implemented, (2) RTCP is not always treated similarly to RTP on an IP network, and (3) the cycle of round-trip measurement coincides with the process cycle of another RTCP element. Round-trip measurement is to measure a round-trip time until a packet originated from a given terminal arrives at another terminal and a response to the packet is sent back.
Conventionally, to measure the round-trip time in the IP network, special packets which contain measurement data, such as RTCP and ICMP (Internet Control Message Protocol), must be generated.
However, a conventional delay measurement method suffers the following problems. (1) A dedicated addition processing block is necessary to generate a special packet. (2) When a special packet is sent to an apparatus which does not support it, the load of a reception process by the incompatible apparatus increases. (3) A special packet cannot pass depending on the settings of the NAT (Network Address Translation), firewall, or router, or may be processed differently from an RTP stream to be measured because priority is given to different traffics.